Guest Water Molecules Research Articles

Manganese(II) and cobalt(II) complexes based on pyridyl diimide: in situ ligand formation, crystal structures, and sorption properties

Two complexes, namely {[Mn(L1)2(H2O)2]·0.5H2O} n (1) and {[Co(L2)(H2O)2]·4H2O} n (2), (L1,1,3-dioxo-2-pyridin-3-ylmethyl-6-[(pyridin-3-ylmethyl)-carbamoyl]-2,3-dihydro-1H-isoindole-5-carboxylic acid; L2,2,5-bis-[(pyridine-3-yl methyl)-carbamoyl]-terephthalic acid), were synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, and X-ray single-crystal structure analysis. The ligands HL1 and HL2 were formed in situ by the hydrolysis of N,N′-bis(3-pyridylmethyl)-pyromellitic diimide (L). Apparently, Mn2+ acts as an asymmetric catalyst, such that a new asymmetric pyridinecarboxylate derivative ligand L1 is formed, while Co2+ acts as a symmetric catalyst, giving the pyridinedicarboxylate derivative ligand L2. Complex 1 has a 1D double-chain structure, in which the adjacent chains are arranged in parallel arrays through π···π interactions, resulting in a 2D supramolecular framework. Complex 2 has a grid (4,4)-sql net structure in an edge-to-edge arrangement through hydrogen bonds between adjacent layers, forming a 3D supramolecular framework containing 1D channels to accommodate water guest molecules. The thermal stabilities of both complexes and ethanol adsorption properties of complex 2 were investigated. 1D double-chain Mn(II) complex (1) and 2D (4,4) net Co(II) complex (2) were synthesized. The Mn2+ ions have the asymmetric catalysis property, and a new asymmetric pyridinecarboxylates derivative ligand is formed; the Co2+ ions have symmetric catalysis property, giving the pyridinedicarboxylates derivative ligand. The complex 2 allows for stepwise sorption of ethanol.

A magnesium-based bifunctional MOF: Studies on proton conductivity, gas and water adsorption

An alkaline earth metal ion based bi-functional metal-organic framework {[Mg(4,4′-bpdc)(H2O)3](H2O)}n (where 4,4′-bpdc=4,4′-biphenyl dicarboxylate) has been synthesized by simply stirring the precursors in water. The framework crystallizes in orthorhombic Pbca space group. The metal nodes of the complex are bridged by dicarboxylates in μ3-fashion to form corrugated 2D coordination sheets. The neighbouring 2D sheets are further connected by hydrogen bonding interactions between the coordinated water molecules and the carboxylate oxygen atoms to form a 3D supramolecular structure. The small hydrophilic supramolecular pockets of the 3D supramolecular structure are filled by guest water molecules through hydrogen bonding interactions. The framework exhibits proton conductivity of 1.44×10−5Sm−1 at 303K under vacuum and the proton transport in the framework follows the Grotthuss mechanism where the hydrogen bonded network acts as the proton transport pathway. The evacuated material, after removal of both coordinated and guest water molecules, retains its crystallinity but is not isostructural with the original framework. According to N2 adsorption study the BET surface area and the total pore volume of the evacuated material are 39m2g−1 and 0.133ccg−1, respectively. The evacuated material can adsorb (175ccg−1 at P/P0∼0.99) and store (154ccg−1 at P/P0=0.1) a decent amount of water molecules.

A cyanide-bridged heterometallic coordination polymer constructed from square-planar [Ni(CN)4](2-): synthesis, crystal structure, thermal decomposition, electron paramagnetic resonance (EPR) spectrum and magnetic properties.

Square-planar complexes are commonly formed by transition metal ions having a d(8) electron configuration. Planar cyanometallate anions have been used extensively as design elements in supramolecular coordination systems. In particular, square-planar tetracyanometallate(II) ions, i.e. [M(CN)4](2-) (M(II) = Ni, Pd or Pt), are used as good building blocks for bimetallic Hofmann-type assemblies and their analogues. Square-planar tetracyanonickellate(II) complexes have been extensively developed with N-donor groups as additional co-ligands, but studies of these systems using O-donor ligands are scarce. A new cyanide-bridged Cu(II)-Ni(II) heterometallic compound, poly[[diaquatetra-μ2-cyanido-κ(8)C:N-nickel(II)copper(II)] monohydrate], {[Cu(II)Ni(II)(CN)4(H2O)2]·H2O}n, has been synthesized and characterized by X-ray single-crystal diffraction analyses, vibrational spectroscopy (FT-IR), thermal analysis, electron paramagnetic resonance (EPR) and magnetic moment measurements. The structural analysis revealed that it has a two-dimensional grid-like structure built up of cationic [Cu(H2O)2](2+) and anionic [Ni(CN)4](2-) units connected through bridging cyanide ligands. The overall three-dimensional supramolecular network is expanded by a combination of interlayer O-H...N and intralayer O-H...O hydrogen-bond interactions. The first decomposition reactions take place at 335 K under a static air atmosphere, which illustrates the existence of guest water molecules in the interlayer spaces. The electron paramagnetic resonance (EPR) spectrum confirms that the Cu(II) cation has an axial coordination symmetry and that the unpaired electrons occupy the d(x(2)-y(2)) orbital. In addition, magnetic investigations showed that antiferromagnetic interactions exist in the Cu(II) atoms through the diamagnetic [Ni(CN)4](2-) ion.

Coordination Chemistry and Structural Dynamics of a Long and Flexible Piperazine-Derived Ligand.

A long and highly flexible internally functionalized dipyridyl ligand α,α'-p-xylylenebis(1-(4-pyridylmethylene)-piper-4-azine), L, has been employed in the synthesis of a series of coordination polymer materials with Co(II), Cd(II), and Ag(I) ions. In poly-[Cd(L)(TPA)] 1 and poly-[Co(L)(IPA)], 2, (TPA = terephthalate, IPA = isophthalate) the ligand adopts a similar linear conformation to that seen in the structure of the unbound molecule and provides a long (2.6 nm) metal-metal bridging distance. Due to the mismatch of edge lengths with that provided by the carboxylate coligands, geometric distortions from the regular dia and (4,4) network geometries for 1 and 2, respectively, are observed. In poly-[Ag2(CF3SO3)2(L)], 3, the ligand coordinates through both pyridine groups and two of the four piperazine nitrogen donors, forming a high-connectivity 2-dimensional network. The compound poly-[Ag2(L)](BF4)2·2MeCN, 4, a porous 3-dimensional cds network, undergoes a fascinating and rapid single-crystal-to-single-crystal rearrangement on exchange of the acetonitrile guests for water in ambient air, forming a nonporous hydrated network poly-[Ag2(L)](BF4)2·2H2O, 5, in which the well-ordered guest water molecules mediate the rearrangement of the tetrafluoroborate anions and the framework itself through hydrogen bonding. The dynamics of the system are examined in greater detail through the preparation of a kinetic product, the dioxane-solvated species poly-[Ag2(L)](BF4)2·2C4H8O2, 6, which undergoes a slow conversion to 5 over the course of approximately 16 h, a transition which can be monitored in real time. The reverse transformation can also be observed on immersing the hydrate 5 in dioxane. The structural features and physical properties of each of the materials can be rationalized based on the flexible and multifunctional nature of the ligand molecule, as well as the coordination behavior of the chosen metal ions.

Magnetic properties of some transition-metal Prussian Blue Analogs with composition M[M(C,N)]·xHO

Abstract Magnetic data are reported for Prussian Blue Analogs (PBAs) of composition M 3 [M ′ (C,N) 6 ] 2 ·xH 2 O , where M = Mn, Co, Ni or Cu and M ′ = Cr, Fe or Co and x is the number of water molecules per unit cell. PBAs crystallize in cubic framework structures, which consist of alternating M III N 6 and M II C 6 octahedra. Occupancies of the octrahedra are not perfect: they may be empty and the charges are balanced by the oxygen atoms originating from guest water molecules at the lattice site ( C or N site) or the interstitial site (between the octahedrals) of the unit cell. Large crystal-field splittings due to the octrahedral environment results in a combination of low- or high-spin configurations of localized magnetic bivalent and trivalent 3d moments. The magnetic susceptibility of studied PBAs follows the Curie–Weiss behavior in the paramagnetic region up to room temperature. Moreover, the data provide evidence for a long-range magnetic ground state for most metal hexacyanochromates and all metal hexacyanoferrates, while hexacyanocobaltates remain paramagnetic down to the lowest temperature measured (2 K). For all compounds, the effective magnetic moments determined from experiments were found to be in reasonable agreement with predicted combinations of high- and low-spin moments.

Transformations of lead 1,3-propylenediaminetetraacetate to its MOF products for the selective adsorption of methanol

Water soluble coordination polymer of potassium lead 1,3-propylenediaminetetraacetate {K4[Pb2(1,3-pdta)2]·6H2O}n (1) and its insoluble products {[Pb(1,3-H2pdta)(H2O)]·2H2O}n (2), {[Pb2(1,3-pdta)(H2O)4]·4H2O}n (3) and [Pb2(1,3-pdta)(H2O)2]n (4) were obtained from the direct reactions of lead nitrate with 1,3-propylenediaminetetraacetic acid in different conditions (1,3-H4pdta=1,3-propylenediaminetetraacetic acid). The former 1 could be converted to the insoluble products of {[Pb2(1,3-pdta)(H2O)4]·4H2O}n (3) and [Pb2(1,3-pdta)(H2O)2]n (4) in weak acidic solution. The complexes have been full characterized by EA, FT-IR, solution and solid state 13C NMR spectra, thermogravimetric and structural analyses. Interestingly, 3 contains a unique (H2O)26 cluster and a 5.2Å pore after eliminating the guest water molecules, which exhibits reversible adsorption for methanol. This is confirmed by PXRD and solid state 13C NMR analyses. Nano-confined methanol in microporous structure has been observed based on the large downfield shift of 13C NMR signal (Δδ 9.72ppm), attributing to the methyl group in methanol.

Hydration-dependent anomalous thermal expansion behaviour in a coordination polymer.

A coordination polymer is shown to possess anomalous anisotropic thermal expansion. Guest water molecules present in the as-synthesised material can be removed upon activation without loss of crystal singularity. The fully dehydrated form shows considerably different thermal expansion behaviour as compared to the hydrate.

Synthesis, Characterization and X-Ray Structure of a Ba(II)/Ag(I)/Cr(III)-Oxalate Salt with Water-Filled Nanochannels

A novel mixed barium(II)/silver(I)/chromium(III) oxalate salt, Ba0.5Ag2[Cr(C2O4)3]·5H2O (1), with open architecture has been synthesized in water and characterized by elemental analysis, vibrational and electronic spectra, and single crystal X-ray structure determination. Compound 1 crystallizes in a monoclinic space group C2/c, with unit cell parameters a = 18.179(3), b = 14.743(2), c = 12.278(2)A, β = 113.821(3), V = 3010.34(90) A3, Z = 8. The structure is characterized by a network of anionic [Cr(C2O4)3]3- units connected through the O atoms of the oxalates to Ba2+ and Ag+ sites, forming a three-dimensional coordination polymer with one-dimensional isolated nanochannels parallel to the c axis, and encapsulating hydrogen-bonded guest water molecules. The bulk structure is consolidated by O–H···O bridgings within the nanochannels and by coulombic interactions.

A dendrimer facilitates resonance energy transfer between hydrophobic aromatic guest molecules in water

A water soluble third generation poly(alkyl aryl ether) dendrimer was examined for its ability to solubilize hydrophobic polyaromatic molecules in water and facilitate non-radiative resonance energy transfer between them. One to two orders of magnitude higher aqueous solubilities of pyrene (PY), perylene (PE), acridine yellow (AY) and acridine orange (AO) were observed in presence of a defined concentration of the dendrimer. A reduction in the quantum yield of the donor PY* emission and a partial decrease in lifetime of the donor excited state revealed the occurrence of energy transfer from dendrimer solubilized excited PY to ground state PE molecules, both present within a dendrimer. The energy transfer efficiency was estimated to be ∼61%. A cascade resonance energy transfer in a three component system, PY*-to-PE-to-AY and PY*-to-PE-to-AO, was demonstrated through incorporation of AY or AO in the two-component PY–PE system. In the three-component system, excitation of PY resulted in emission from AY or AO via a cascade energy transfer process. Careful choice of dye molecules with good spectral overlap and the employment of dendrimer as the medium enabled us to expand absorption-emission wavelengths, from ∼330 nm to ∼600 nm in aqueous solution.

Crystal structure of bis-p-anizidinegossypol with an unknown solvate.

The title compound, C44H44N2O8, (systematic name: 1,1',6,6'-tetra-hydroxy-5,5'-diisopropyl-8,8'-bis-{[(4-meth-oxy-phen-yl)iminium-yl]meth-yl}-3,3'-dimethyl-2,2'-bi-naphthalene-7,7'-diolate) has been obtained by the addition of p-anizidine to gossypol dissolved in di-chloro-methane. In the solid state, the title compound exists in the enamine or quinoid form. The two naphthyl moieties are inclined to one another by 72.08 (5)°. The pendant phenyl rings are inclined at 22.26 (14) and 23.86 (13)° to the corresponding naphthyl rings. In the crystal, mol-ecules are incorporated into layers through inversion-related pairs of O-H⋯O inter-actions [graph sets R 2 (2)(20) and R 2 (2)(10)] and translation-related O-H⋯O inter-actions [graph set C(15)]. The packing of these layers in the crystal structure gives rise to channels in the [011] direction, with hydro-phobic inter-actions occurring between adjacent layers. The channels are 5-7 Å wide, and the void volume of each cell is 655 Å(3), corresponding to 26.6% of the cell volume. Disordered guest mol-ecules, probably solvent and water mol-ecules, occupy these voids of the crystal; their contribution to the scattering was removed with the SQUEEZE routine [Spek (2015 ▸). Acta Cryst. C71, 9-18] of PLATON [Spek (2009 ▸). Acta Cryst. D65, 148-155].

Preparation of zinc oxide nanoparticles from nanoporous metal–organic framework with one-dimensional channels occupied with guest water molecules

A new nanoporous metal–organic framework Zn2(NDC)2(DMF)2·(H2O)4 (1·DMF·H2O) [H2NDC=2,6-naphthalene dicarboxylic acid and DMF=N,N′-dimethylformamide], with guest water molecules has been synthesized and characterized. This MOF is made up of a stacked arrangement of four-connected layers. Stacked arrangement of layers results in formation of nanoporous channels. The thermal stabilities of 1·DMF·H2O and 1·DMF were studied by TGA (thermo gravimetric analyses). The host and the apohost frameworks of 1·DMF·H2O, 1·DMF and 1 were used for preparation of ZnO nanomaterials. With calcination of the host framework of 1·DMF·H2O, ZnO nanoparticles can be fabricated. By the same process on the apohost frameworks of 1·DMF and 1, agglomerated nanoparticles of ZnO were formed.

Racemic and homochiral coordination polymers based on carboxylates of different lengths

Three coordination polymers, {[Ag2(R-PHBU)(S-PHBU)(bpp)2]·H2O}n (1, racemic), {[Ag2(R-PHSU)0.5(S-PHSU)0.5(bpp)2]·2H2O}n (2, racemic), and {[Ag2(CHDA)(bpp)2]·9H2O}n (3, homochiral) (HPHBU = 2-phenylbutyric acid, H2PHSU = 2-phenylsuccinic acid, H2CHDA = 1,1-cyclohexanediacetic acid, bpp = 1,3-bis(4-pyridyl)propane), have been synthesized by solution reactions of Ag(I) with bpp and rac-PHBU−, rac-PHSU2−, or CHDA2−. Single-crystal X-ray diffraction reveals that all three complexes feature “AgAg” subunits extended by bpp ligands in two-dimensional (2-D) cation layers, which are embedded by the PHBU−, PHSU2−, or CHDA2− ligands of different lengths. Adjacent 2-D layers with pillar-shaped fillers are mutually interdigitated to 3-D H-bonded supramolecular coordination polymers with 1-D pores. As the length of the pillar-shaped fillers increases from 5.6, 6.4 to 7.3 Å, the dimensions of the pores range from 5.0 × 3.7 Å (narrow slit), 8.7 × 5.6 Å (elliptical) to 13.4 × 6.8 Å (quadrangular), and the solvent-accessible void volumes range from 3.6, 31.8 to 36.4% of the crystal volumes. The 1-D pores are filled with guest water molecules. The guest water molecules in 1 are discrete. Centrosymmetric water tapes and chiral right-handed 21 helical water tapes are observed in 2 and 3, respectively. Thermal and photoluminescent properties, as well as lead(II) adsorption, are also discussed.

A Three-Dimensional Dynamic Metal-Organic Framework with Fourfold Interpenetrating Diamondoid Networks and Selective Adsorption Properties.

A three-dimensional metal-organic framework (1) with fourfold interpenetrating diamondoid networks was constructed using a macrocyclic nickel(II) complex and a tetracarboxylic ligand 4,4',4″,4‴-(cyclohexane-1,2-diyibis(azanetriyl))tetrakis(methylene)tetrabenzoic acid as building blocks. Despite the fourfold interpenetration, 1 possesses one-dimensional channels that are occupied by water and CH3CN guest molecules. Once the guest molecules were removed, the framework and pores in desolvated 1 are dynamic with large adsorption hysteresis loops, which exhibit selective gas adsorption for CO2 at 195 K over N2 and H2 at 77 K and selective adsorption for methanol, ethanol, and n-propanol over isopropanol at 298 K.

Formation of a Syndiotactic Organic Polymer Inside a MOF by a [2+2] Photo-Polymerization Reaction.

Getting suitable crystals for single-crystal X-ray crystallographic analysis still remains an art. Obtaining single crystals of metal-organic frameworks (MOFs) containing organic polymers poses even greater challenges. Here we demonstrate the formation of a syndiotactic organic polymer ligand inside a MOF by quantitative [2+2] photopolymerization reaction in a single-crystal-to-single-crystal manner. The spacer ligands with trans,trans,trans-conformation in the pillared-layer MOF with guest water molecules in the channels, undergo pedal motion to trans,cis,trans-conformation prior to [2+2] photo-cycloaddition reaction and yield single crystals of MOF containing two-dimensional coordination polymers fused with the organic polymer ligands. We also show that the organic polymer in the single crystals can be depolymerized reversibly by cleaving the cyclobutane rings upon heating. These MOFs also show interesting photoluminescent properties and sensing of small organic molecules.

Formation of a Syndiotactic Organic Polymer Inside a MOF by a [2+2] Photo‐Polymerization Reaction

AbstractGetting suitable crystals for single‐crystal X‐ray crystallographic analysis still remains an art. Obtaining single crystals of metal–organic frameworks (MOFs) containing organic polymers poses even greater challenges. Here we demonstrate the formation of a syndiotactic organic polymer ligand inside a MOF by quantitative [2+2] photopolymerization reaction in a single‐crystal‐to‐single‐crystal manner. The spacer ligands with trans,trans,trans‐conformation in the pillared‐layer MOF with guest water molecules in the channels, undergo pedal motion to trans,cis,trans‐conformation prior to [2+2] photo‐cycloaddition reaction and yield single crystals of MOF containing two‐dimensional coordination polymers fused with the organic polymer ligands. We also show that the organic polymer in the single crystals can be depolymerized reversibly by cleaving the cyclobutane rings upon heating. These MOFs also show interesting photoluminescent properties and sensing of small organic molecules.

Understanding DABCO Nanorotor Dynamics in Isostructural Metal-Organic Frameworks.

Flexible framework dynamics present in the subset of metal-organic frameworks known as soft porous crystals give rise to interesting structural properties that are unique to this class of materials. In this work, we use experiments and molecular simulation to understand the highly dynamic nanorotor behavior of the 1,4-diazabicyclo[2.2.2]octane (DABCO) ligand in the pillared Zn-DMOF and Zn-DMOF-TM (TM = tetramethyl) structures. While DABCO is known to be displaced in the presence of water in the parent Zn-DMOF structure, the Zn-DMOF-TM variation is highly stable even after adsorbing significant amounts of water vapor. The dynamics of DABCO in the presence of water guest molecules is therefore also explored in the Zn-DMOF-TM structure via in situ NMR and IR experiments. This analysis shows that the rotational motion of the DABCO linkers is dependent on water content, but not a likely source of water instability because the dynamics are fast and largely unaffected by the presence of methyl functional groups.

Interaction of the Trinuclear Triangular Secondary Building Unit [Cu3(μ3-OH)(μ-pz)3]2+ with 4,4′-Bipyridine. Structural Characterizations of New Coordination Polymers and Hexanuclear CuII Clusters. 2°

By reacting 4,4′-bipyridine (bpy) with selected trinuclear triangular CuII complexes, [Cu3(μ3-OH)(μ-pz)3(RCOO)2(LL′)] [pz = pyrazolate anion; R = CH3, CH3CH2, CH2═CH, CH2═C(CH3); L, L′ = Hpz, H2O, MeOH] in MeOH, the substitution of monotopic ligands by ditopic bpy was observed. Depending on the stoichiometric reaction ratios, different compounds were isolated and structurally characterized. One- and two-dimensional coordination polymers (CPs), as well as two hexanuclear CuII clusters were identified. One of the hexanuclear clusters self-assembles into a supramolecular three-dimensional structure, and its crystal packing shows the presence of two intersecting channels, one of which is almost completely occupied by guest bpy, while in the second one guest water molecules are present. This compound also shows a reversible, thermally induced, single-crystal-to-single-crystal transition.

Anion binding by biotin[6]uril in water.

In this contribution we show that the newly discovered 6 + 6 biotin-formaldehyde macrocycle Biotin[6]uril binds a variety of anionic guest molecules in water. We discuss how and why the anions are bound based on data obtained using NMR spectroscopy, mass spectrometry, isothermal titration calorimetry (ITC), computational calculations and single crystal X-ray crystallography.

Benzene absorption in a protuberant-grid-type zinc(ii)–organic framework triggered by the migration of guest water molecules

The 2D protuberant-grid-type Zn(II)-organic framework consists of unusual racemic interdigitated bilayers and comprises a 3D intersecting channel system. The framework is thermally stable and the channels contain multiple water aggregates. Accompanying the migration of guest water molecules, only the specific channels in the bilayers along the b axis can easily and efficiently absorb guest benzene molecules in a regular manner.

A resistance-switchable and ferroelectric metal-organic framework.

The ever-emerging demands on miniaturization of electronic devices have pushed the development of innovative materials with desired properties. One major endeavor is the development of organic- or organic-inorganic hybrid-based electronics as alternatives or supplements to silicon-based devices. Herein we report the first observation of the coexistence of resistance switching and ferroelectricity in a metal-organic framework (MOF) material, [InC16H11N2O8]·1.5H2O, denoted as RSMOF-1. The electrical resistance of RSMOF-1 can be turned on and off repeatedly with a current ratio of 30. A first-principles molecular dynamics simulation suggests that the resistive switching effect is related to the ferroelectric transition of N···H-O···H-N bridge-structured dipoles of the guest water molecules and the amino-tethered MOF nanochannel. The discovery of the resistive switching effect and ferroelectricity in MOFs offers great potential for the physical implementation of novel electronics for next-generation digital processing and communication.